package com.chenjia.proto.converter.utils;


import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;

/**
 * Contains static utility methods pertaining to primitive types and their corresponding wrapper
 * types.
 *
 * @author Kevin Bourrillion
 * @since 1.0
 */

public final class Primitives {
	private Primitives() {
	}

	/**
	 * A map from primitive types to their corresponding wrapper types.
	 */
	private static final Map<Class<?>, Class<?>> PRIMITIVE_TO_WRAPPER_TYPE;

	/**
	 * A map from wrapper types to their corresponding primitive types.
	 */
	private static final Map<Class<?>, Class<?>> WRAPPER_TO_PRIMITIVE_TYPE;

	// Sad that we can't use a BiMap. :(

	static {
		Map<Class<?>, Class<?>> primToWrap = new HashMap<Class<?>, Class<?>>(16);
		Map<Class<?>, Class<?>> wrapToPrim = new HashMap<Class<?>, Class<?>>(16);

		add(primToWrap, wrapToPrim, boolean.class, Boolean.class);
		add(primToWrap, wrapToPrim, byte.class, Byte.class);
		add(primToWrap, wrapToPrim, char.class, Character.class);
		add(primToWrap, wrapToPrim, double.class, Double.class);
		add(primToWrap, wrapToPrim, float.class, Float.class);
		add(primToWrap, wrapToPrim, int.class, Integer.class);
		add(primToWrap, wrapToPrim, long.class, Long.class);
		add(primToWrap, wrapToPrim, short.class, Short.class);
		add(primToWrap, wrapToPrim, void.class, Void.class);

		PRIMITIVE_TO_WRAPPER_TYPE = Collections.unmodifiableMap(primToWrap);
		WRAPPER_TO_PRIMITIVE_TYPE = Collections.unmodifiableMap(wrapToPrim);
	}

	private static void add(Map<Class<?>, Class<?>> forward, Map<Class<?>, Class<?>> backward, Class<?> key, Class<?>
			value) {
		forward.put(key, value);
		backward.put(value, key);
	}

	/**
	 * Returns an immutable set of all nine primitive types (including {@code
	 * void}). Note that a simpler way to test whether a {@code Class} instance is a member of this
	 * set is to call {@link Class#isPrimitive}.
	 *
	 * @return class set
	 * @since 3.0
	 */
	public static Set<Class<?>> allPrimitiveTypes() {
		return PRIMITIVE_TO_WRAPPER_TYPE.keySet();
	}

	/**
	 * Returns an immutable set of all nine primitive-wrapper types (including {@link Void}).
	 *
	 * @return class set
	 * @since 3.0
	 */
	public static Set<Class<?>> allWrapperTypes() {
		return WRAPPER_TO_PRIMITIVE_TYPE.keySet();
	}

	/**
	 * Returns {@code true} if {@code type} is one of the nine primitive-wrapper types, such as
	 * {@link Integer}.
	 *
	 * @param type class
	 * @return true if wrapped type
	 * @see Class#isPrimitive
	 */
	public static boolean isWrapperType(Class<?> type) {
		return WRAPPER_TO_PRIMITIVE_TYPE.containsKey(type);
	}

	/**
	 * Returns the corresponding wrapper type of {@code type} if it is a primitive type; otherwise
	 * returns {@code type} itself. Idempotent.
	 * <pre>
	 *     wrap(int.class) == Integer.class
	 *     wrap(Integer.class) == Integer.class
	 *     wrap(String.class) == String.class
	 * </pre>
	 *
	 * @param type type
	 * @param <T>  class
	 * @return itself.
	 */
	public static <T> Class<T> wrap(Class<T> type) {

		// cast is safe: long.class and Long.class are both of type Class<Long>
		@SuppressWarnings("unchecked")
		Class<T> wrapped = (Class<T>) PRIMITIVE_TO_WRAPPER_TYPE.get(type);
		return (wrapped == null) ? type : wrapped;
	}

	/**
	 * Returns the corresponding primitive type of {@code type} if it is a wrapper type; otherwise
	 * returns {@code type} itself. Idempotent.
	 * <pre>
	 *     unwrap(Integer.class) == int.class
	 *     unwrap(int.class) == int.class
	 *     unwrap(String.class) == String.class
	 * </pre>
	 *
	 * @param type type
	 * @param <T>  class
	 * @return itself.
	 */
	public static <T> Class<T> unwrap(Class<T> type) {

		// cast is safe: long.class and Long.class are both of type Class<Long>
		@SuppressWarnings("unchecked")
		Class<T> unwrapped = (Class<T>) WRAPPER_TO_PRIMITIVE_TYPE.get(type);
		return (unwrapped == null) ? type : unwrapped;
	}
}
